Polymeric thickeners for aqueous compositions

ABSTRACT

A process of preparing a concentrate which is useful as a thickener for aqueous compositions is provided. The process comprises obtaining a solution of an associative thickener compound in an organic solvent capable of forming a low boiling azeotrope with water. The solution is essentially free of water at this point and is at a temperature above the boiling point of said low boiling azeotrope. Water is added to said solution and an azeotrope of water and said organic solvent is distilled. The rate of addition of water is sufficient to replace said azeotrope with water, but is insufficient to cause a second phase to form in the resulting mixture of said solution and said water. The process yields a concentrate of an associative thickener in water, which concentrate is essentially free of volatile organic solvents.

This is a continuation application of Ser. No. 08/901,579, filed Jul.28, 1997.

BENEFIT OF EARLIER FILING DATE UNDER 37 CFR 1.78(A)(4)

This application claims the benefit of earlier filed and copendingprovisional application Ser. No. 60/024,101 filed on Aug. 27, 1996.

FIELD OF THE INVENTION

This invention relates to a process of preparing a concentrate ofpolymeric compounds which are useful as thickeners for aqueouscompositions, especially emulsion polymer latexes.

BACKGROUND ART

Many aqueous systems require thickeners in order to be useful forvarious types of applications. Such aqueous-based systems as cosmetics,protective coatings for paper and metal, printing inks, and latex paintsall require the incorporation of thickeners in order to have the properrheological characteristics for their particular uses. Many substancesuseful as thickeners are known in the art. These include naturalpolymers such as casein and alginates, and synthetic materials such ascellulose derivatives, acrylic polymers, and polyurethane polymers.

Associative thickeners are so called because the mechanism by which theythicken may involve hydrophobic associations between the hydrophobicspecies in the thickener molecules and other hydrophobic surfaces,either on other thickener molecules, or on molecules in the system to bethickened. The different types of associative thickeners include, butare not limited to, polyurethanes, hydrophobically-modified alkalisoluble emulsions, hydrophobically modified hydroxyethyl cellulose orother products, and hydrophobically modified polyacrylamides.

The molecular weight and HLB of these associative thickeners, whichusually are water soluble or dispersible polymers, is chosen to besufficiently high to impart desired rheological properties to an aqueouscomposition containing the thickener. Advantageously, the water-solublepolymer has a molecular weight sufficiently high such that a solutioncontaining up to 2-3 weight percent of this polymer will exhibit aviscosity of at least 5,000, preferably at least 15,000, and mostpreferably at least 20,000 centipoises (as measured on a Brookfieldviscometer with a number 3 spindle at 10 RPM at 25° C.). As explainedabove, a variety of polymeric materials may be used as a water-solublepolymer, including cellulose ethers, polyacrylamides, sulfonatedpolystyrenes, copolymers of acrylic acid, hydroxypropylated guar, andthe like.

Such polymers tend to be quite viscous when present in highconcentration in an aqueous solution. Reduction of viscosity with addedagents, e.g., organic cosolvents is possible, but the use of viscosityreducing agents can pose environmental problems (e.g., contribute tovolatile organic compound content) or performance problems (e.g., addedsurfactants can detract from the performance of coating of a latex whichcontains the thickener).

SUMMARY OF THE INVENTION

This invention relates to process of preparing a concentrate which isuseful as a thickener for aqueous compositions, particularly latexpaints, comprising:

obtaining a solution of an associative thickener compound in an organicsolvent capable of forming a low boiling azeotrope with water, saidsolution being essentially free of water, at a temperature above theboiling point of said low boiling azeotrope,

adding water to said solution and distilling an azeotrope of water andsaid organic solvent, wherein the rate of addition of water issufficient to replace said azeotrope with water, but is insufficient tocause a second phase to form in the resulting mixture of said solutionand said water.

It has been found that if the rate of water addition is too low, e.g.,all of the water added is allowed to distill as the azeotrope, theresulting mixture will become too viscous to be handled, and that if therate of water addition is too fast, an oil-in-water emulsion will form(as evidenced by a milky appearance, typically accompanied by anincrease in viscosity making the mixture too viscous to be handled andan increase in volume due to foaming). The oil-in-water emulsion makesdistillation of the organic solvent extremely difficult, if notimpractical. Thus, the rate of water addition should be controlled to atleast replace the azeotrope formed, but to maintain the bulk of thepolymer in true solution. The product is typically essentially free ofvolatile organic solvents (e.g., none as measured by ASTM MethodD2369-90).

Preferred associative thickener compounds have the formula I:

    R.sup.1 --(O--A).sub.a --B.sup.1 --R.sup.2 --(B.sup.2 --R.sup.3).sub.d --(B.sup.3 --(A'--O).sub.b-f --(A'--B.sup.4).sub.f --R.sup.4 --(B.sup.5 --R.sup.5).sub.e).sub.n --B.sup.6 --(A"O).sub.c--R.sup.6

wherein:

R¹ and R⁶ are monovalent hydrophobic groups independently selected fromthe group consisting of an aliphatic group, a substituted aliphaticgroup, an aromatic group, and a substituted aromatic group;

R² and R⁴ are independently selected from the group consisting ofaliphatic, substituted aliphatic, aromatic, or substituted aromaticradicals, each radical being divalent or trivalent;

R³ and R⁵ are independently selected from hydrogen, lower alkyl andlower aralkyl;

B¹, B², B³, B⁴, B⁵, and B⁶ are linking groups independently selectedfrom the group consisting of an oxygen atom (to form the ether linkage--O--), a carboxylate group (to form an ester linkage R² --C(O)--O--and/or R⁴ --C(O)--O--), an amino group (to form the amine linkage R²--N(R)-- and or R⁴ --N(R)--, wherein R is hydrogen, lower alkyl, loweraralkyl, or lower acyl), and an amido group (to form the amide linkageR² --N(R)--C(O)-- and/or R⁴ --N(R)--C(O)--, wherein R is hydrogen, loweralkyl, lower aralkyl, or lower acyl);

each of a, b, c, d, e, f, and n are integers, wherein each of a and care independently any integer from greater than 20 to about 200; b isany integer from greater than 20 to about 450; d, e, and f are zero or1; and n is any integer from 1 to about 5; and

each of A, A', and A" is independently an ethylene, 1,2-propylene,1,2-butylene unit or combinations thereof.

In preferred compounds, each of R¹ and R⁶ is independently an aliphatic,substituted aliphatic, aromatic, or substituted aromatic radical havingfrom 4 to about 50 carbon atoms; each of B¹ -B⁶ is an oxygen atom; R²and R⁴ are both either propanetriyl or meta-xylyl; d and e are either(i) both zero (e.g., when R² and R⁴ are both meta-xylyl) or (ii) both 1and R³ and R⁵ are hydrogen, methyl or benzyl (e.g., when R² and R⁴ areboth propanetriyl); f is zero; each of A, A', and A" are ethylene, n is1, b is from about 50 to about 450, more preferably from about 90 toabout 450, and the values of a and c independently range from about 50to about 150.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention may be useful in the context of a wide variety ofthe associative thickeners discussed above, the preferred associativethickeners for use herein are described as follows. In regard to formulaI, the abbreviations A, A', and A" stand for the ethylene group (--CH₂CH₂ --), the 1,2-propylene group --(CH₂ CH(CH₃)--), or the 1,2-butylenegroup (--CH(CH₂ CH₃)CH₂ --) or combinations thereof. Each of thesubscripts a, b, c, f, and n are independently any integer as set forthabove. One of ordinary skill in the art will appreciate that formixtures of pure compounds, the subscripts a, b, c, f, and n will havenon-integer values to reflect the fact that they represent the averagedegree of polymerization, e.g., n is from 0.5 to 4.5, preferably 0.5 to1.5.

R² and R⁴ are aliphatic, substituted aliphatic, aromatic, or substitutedaromatic radical having a valence of from 2 or 3. Such aliphaticradicals include any di- or trivalent: (a) straight chain and branchedalkyl radicals having from 2 to about 50 carbon atoms (preferablydivalent or trivalent alkylene radicals having from 2 to 10 carbonatoms); (b) cycloalkyl radicals having from 4 to about 20 carbon atoms;(c) straight chain and branched alkenyl radicals having from 2 to about40 carbon atoms; (d) cycloalkenyl radicals having from 5 to about 20carbon atoms; (e) straight chain and branched alkynyl radicals havingfrom 2 to about 30 carbon atoms; cycloalkynyl radicals having from 6 toabout 20 carbon atoms; and (f) aralkyl radicals (i.e., alkyl radicalshaving aromatic groups as pendent substituents or linking alkylenegroups) having at least 2 aliphatic carbon atoms along with an aromaticgroup, e.g., meta-xylyl wherein methylene groups are linked by abenzenoid group). Aliphatic radicals also include those above-mentionedaliphatic radicals which contain one or more heteroatoms substituted forone or more hydrogen atoms. The heteroatoms include the halogens,nitrogen, sulfur, oxygen, and phosphorus or groups of heteroatoms suchas nitro, sulfonic acid, C₁₋₁₀ alkyl sulfonate ester, sulfoxide,sulfone, phosphoryl, trihalomethyl, and the like. For purposes of thisinvention, it is understood that aliphatic includes cycloaliphatic andheterocycloaliphatic wherein the heteroatoms are nitrogen, oxygen,sulfur, and phosphorus.

An aromatic radical is any benzenoid or non-benzenoid aromatic radicalhaving a valence of 2 to 8. A non-benzenoid aromatic radical includescarbocyclic and heterocyclic aromatic radicals. For purposes of thisinvention, a substituted aromatic radical is any benzenoid ornon-benzenoid aromatic radical having a valence of from 2 to 6 whereinone or more hydrogen atoms is replaced by an atom or a group of atomsother than hydrogen including the halogens, nitrogen, sulfur, oxygen,and phosphorus or groups of heteroatoms such as nitro, sulfonic acid,C₁₋₁₀ alkyl sulfonate ester, sulfoxide, sulfone, phosphoryl,trihalomethyl, and the like.

The abbreviations NP, DNP, LA, and TD stand for nonylphenoxy,dinonylphenoxy, lauryl, and tridecyl, respectively. R¹ and R⁶ aremonovalent radicals, typically having from about 6 to about 50 carbonatoms. The use of a hydrophobic alcohol to form the ends of the compoundof formula I described above results in the formation of hydrophobicether residues as R¹ and R⁶. A hydrophobic group is any group whichcontributes to the water insolubility of the ether residue.Unsubstituted aliphatic groups having at least 6 carbon atoms, aromaticgroups having 6 or more carbon atoms and groups which contain bothaliphatic and aromatic moieties are hydrophobic. Examples of usefulhydrophobic ether residues include but are not limited to, tolyl, hexyl,ethylphenyls, heptyl, cumyl, propylphenyls, octyl, butylphenyls,nonylphenyls, pentylphenyls, decyl, isohexylphenyls, n-hexylphenyls,n-undecyl, heptylphenyls, lauryl, octylphenyls, isononylphenyls,n-nonylphenyls, tetradecyl, decylphenyls, n-undecylphenyls, hexadecyl,isododecylphenyls, n-dodecylphenyls, stearyl, n-tetradecylphenyls,hexadecylphenyls, and isooctadecylphenyls. Preferred hydrophobes are thenonylphenyl, dinonylphenyl, lauryl, and tridecyl groups.

The use of the term "lower" to modify "alkyl" shall mean an alkyl grouphaving from 1 to about 4 carbon atoms, e.g., methyl, ethyl, n-propyl,isopropyl, and tert-butyl. Further, the term "lower" when used to modify"aralkyl" shall mean an alkyl group having from 1 to about 4 carbonatoms substituted with a benzenoid radical, and the term "lower" whenused to modify "acyl" shall mean a carbonyl terminated lower alkyl orlower aralkyl radical.

Each of A, A', and A" groups of formula I represent an ethylene,1,2-propylene, 1,2-butylene unit or combinations thereof such that eachof (A--O)_(a), (A'--O)_(b) and (A"--O)_(c) is a water soluble, or waterdispersible polyether group. The water solubility or waterdispersibility of a polyether group is a function of its molecularstructure and/or its molecular weight. For example, an ethyleneoxy (EO)homopolymer having a molecular weight of about 20,000 daltons or less iswater soluble while a water soluble propyleneoxy (PO) homopolymer has amolecular weight of less than about 700 daltons. The structure of anEO--PO copolymer must be such that it contains at least about 50 wt % ofethyloxy groups to be water soluble. The structure-propertyrelationships of EO and PO polyethers is described in the Encyclopediaof Polymer Science and Engineering, Second Edition, vol. 6, pp. 225-273,(John Wiley and Sons, Inc., 1986), while those of poly PO are describedin vol. 6, page 300. In preferred compounds, the A, A', and A" groupsconsist essentially of ethylene groups, the value of b in formula Iabove is preferably from about 50 to about 450, more preferably fromabout 90 to about 450, and the values of a and c preferably range fromabout 50 to about 150.

The compounds according to the invention are polymeric materials whichcan be made by any process within the purview of those having ordinaryskill in the art. A preferred method is a two-step process, the firststep of which comprises forming a mixture of compounds of the followingformulas: ##STR1## wherein all symbols are as set forth above and underconditions which cause at least a portion of the terminal hydrogen atomsof the hydroxyl groups shown above to ionize leaving alkoxide oxygenatoms. These conditions can be brought about by adding to the mixture astrong base, for example an alkali or alkaline earth metal lower alkylalkoxide, e.g., sodium methoxide. Of course, when B is an amino or amidogroup, the terminal hydroxyl of the compounds of formulas I, II and IIIshould be replaced by an amine nitrogen having the appropriatesubstituents to introduce the desired B and R groups into the molecule.Examples of such amine functional compounds useful to introduce an aminegroup are the polyoxyethyleneamine and polyoxypropyleneamines (availableunder the tradename JEFFAMINE®, from Texaco Chemical Company, Houston,Tex.). Compounds of formula II and IV, but wherein the terminal hydroxyis replaced by an amino nitrogen can be prepared by one of ordinaryskill in the art. For example, compounds of formula II and IV can besubjected to a catalyzed ammoniation (with ammonia, or a loweralkylamine or lower acyl amide) for replacement of the hydroxyl, or to acapping of the hydroxyl with epichlorohydrin followed by ammoniation(with ammonia, or a lower alkylamine or lower acylamide) of theresulting glycidal group.

The second step of the two-step process comprises forming a mixture ofthe product of step one in further admixture with a member selected fromthe group of a di-etherifying agent, a tri-etherifying agent, adi-esterifying agent, a tri-esterifying agent, and a mixture of two ormore of such members. (Of course, when the compounds are amines oramides rather than hydroxyl compounds, the reaction is an alkylation oramidation reaction. To simplify the following description, referencesbelow to etherifying agents or esterifying agents in general should beconstrued as applicable to alkylating agents and amidifying agents,respectively.) This basic reaction can be represented by: ##STR2##wherein Y, Y'and Y" are leaving groups in the case of etherifying agentsor carboxy-functional groups in the case of esterifying agents. (Ofcourse, the hydroxyl groups of the compounds of formulas II, III, and IVare amino or amido groups when B is to be such a linking group. Further,Y--R² --(Y')_(d) --Y" can also be an acetal, ketal, or orthoester, inwhich case Y and Y" are lower alkoxy groups which leave in atransacetalization, transketalization, or transorthoesterification,respectively. This leads to a compound of formula I in which B is anether linking group from these special classes of ethers, i.e., acetals,ketals or orthoesters.)

It should be noted that when all B linkages are to be, for example,ether linkages, then only a di-etherifying agent and/or atri-etherifying agent will be used to the exclusion of any esterifyingagents. Likewise, when all B linkages are to be ester linkages, thenonly a di-esterifying agent and/or a tri-esterifying agent will be usedto the exclusion of any etherifying agents. Similarly, if both d and eare to be zero (i.e., R² and R⁴ are only divalent radicals), then only adi-etherifying agent and/or a di-esterifying agent will be used to theexclusion of any tri-etherifying agents and tri-esterifying agents. Suchetherifying (or alkylating) and esterifying (or amidifying) agents arecapable of reacting with the hydroxyl (or amine or amide groups) oralkoxide oxygens of the reactants II, III and IV, above. These agentswill thus introduce the divalent or trivalent radicals R² and R⁴ intothe molecule. Examples of etherifying (or alkylating) agents are alkylhalides, e.g., divalent compounds (e.g., alpha,alpha'-dichloro-meta-xylene) that introduce a divalent R² and/or R⁴group into the molecule, e.g., through the same mechanism as a classicalWilliamson ether (or amine alkylation) synthesis. When R² and/or R⁴ areto be aromatic radicals, it may be convenient to employ adi-halo-aromatic compound (e.g., di-bromo-benzene) which can bederivatized to the corresponding mono-Grignard reagent and reacted withthe diol reactant of formula III, above (which will cap the diol withether groups R² and/or R⁴ at each end of the diol to form, in the caseof di-bromo-benzene, a bis-bromo-phenyl ether of the diol). This cappedadduct can then be sequentially derivatized in a second Grignardreaction, the product of which can be reacted with reactants of formulasII and IV above, to give a compound of formula I wherein R² and/or R⁴are aromatic groups.

Further examples of etherifying agents include epihalohydrin compounds,(e.g., those of the formula X--CH₂ --CH--(O)--CH₂ wherein X is a leavinggroup, for example a halogen, e.g., chlorine which forms a chloride ionas the leaving group) or a precursor of an epihalohydrin (e.g., acompound of the formula X--CH₂ --CH--(OR³)--CH₂ --X', wherein X' is aleaving group). When this precursor is used, the epihalohydrin, may beformed, at least in part, in situ, or the alkoxide moieties formed instep one may displace both the X and X' groups in an S_(N) 2 reaction.When R³ and/or R⁵ are lower alkyl, then the epihalohydrin compound maybe an ether having the formula X--CH₂ --CH--(OR³)--CH₂ --X', wherein Xand X' are leaving groups and R³ is a lower alkyl group (i.e., C₁ to C₄alkyl, preferably methyl). Alternatively, the reaction mixture may alsocontain an alkylating agent of the formula X"--R³ (e.g., methyl chlorideor benzyl chloride) that can react with the alkoxide radical (orhydroxyl group) formed by opening of the oxirane ring of theepihalohydrin. This alkylating agent would preferably be added with theepihalohydrin compound to reduce the opportunity of a side reaction withthe alkoxide compounds which introduce the R¹ and R⁶ groups into themolecule. Of course, if R³ and R⁵ are different, then a secondepihalohydrin ether having the formula X--CH₂ --CH--(OR⁵)--CH₂ --X'and/or a second alkylating agent having the formula X"--R⁵ must beemployed to introduce the R⁵ group into the molecule.

Examples of esterifying agents include di-basic and tri-basic organicacids, and reactive derivatives thereof, e.g., acid halides, acidanhydrides, and/or lower esters of such di-basic and tri-basic organicacids (all of which have carboxy-functional groups capable of reactingwith the hydroxyl or alkoxide functional compounds of formulas II, III,IV). Because branching is generally undesirable (as discussed below inthe context of the epihalohydrin etherifying agents), if an esterifyingagent is employed, it is preferably only di-basic, e.g., succinic acidor phthalic anhydride. If a tri-basic acid is employed, a lower alkanol(e.g., methanol) can be added to the reaction mixture so that R³ and/orR⁵ will be lower alkyl. (This addition of a lower alkanol is similar tothe chain stopping effect discussed below in the context of alkylhalides used with epihalohydrins). The reaction conditions for theesterification reaction will of course differ from those appropriate foran etherification reaction, Esterification reactions with polybasicacids are discussed in the Encyclopedia of Polymer Science andEngineering, vol. 12, pp. 28-43 (John Wiley and Sons, Inc., New York,N.Y., 1988), the disclosure of which is incorporated herein byreference. The presence of ester linkages is less desirable when thecompound will be used in aqueous compositions that are not at anessentially neutral pH (e.g., from a pH of about 6.5 to about 7.5).Because many latex compositions are formulated to have an alkaline pH(e.g., about pH 9 to about pH 11), compounds of formula I wherein all Blinkages are ether linkages are preferred for their resistance tohydrolysis.

The ratios of the reactants of formulas II, III, and, IV may vary, butwill generally range within 20 mole % to 45 mole % each of the compoundsof formula II and IV (if R¹ and R⁶ are the same, then the amount of thesingle reactant will, thus, be 40 mole % to 90 mole %) and 3 mole % to60 mole %, preferably 10 mole % to 60 mole %, of the compound of formulaIII. The amount of the etherifying or esterifying compound that is thenreacted with the alkoxides may also vary, but will generally range fromabout 0.25:1 to about 1.5:1.0 (preferably about 0.8:1 to 1.2:1)equivalents of etherifying agent or esterifying agent (a divalent agenthaving two equivalents per mole) to hydroxyl equivalent weights of thereactants of formulas II (having one equivalent per mole), III (havingtwo equivalents per mole), and IV (having one equivalent per mole).

It is believed that compositions which contain predominantly compoundsof formula I are superior thickeners compared to compositions whichcontain compounds wherein R³ and/or R⁵ are not hydrogen, lower alkyl, orlower aralkyl, but are larger organic groups. Such larger organic groupscan result from the reaction of a second molecule of epichlorohydrinwith, e.g., the intermediate alkoxide compound of the formula:

    R.sup.1 --(O--A').sub.a O--R.sup.2 --(O.sup.-)--(O--(A'--O).sub.b --R.sup.4 --(OR.sup.5)).sub.n --O--(A"--O).sub.c --R.sup.6

and that this second molecule of epichlorohydrin can react, or mayalready have reacted, with the alkoxide R¹ --(O--A')_(a) O⁻ (or R⁶--(O--A")_(c) --O⁻). In this case, a compound will be formed which has asimilar structure to the compounds of formula I, but in which R³ willthen have the formula:

    --R.sup.2 --(O.sup.-)--(A'O).sub.a --O--R.sup.1

which yields a molecule with significant branching in its molecularstructure. Of course, such branching can also occur at R⁴ wherein R⁵ issimilarly replaced by the reaction product of a second molecule ofepichlorohydrin and an alkoxide. (If a tri-esterifying agent is used,then the branching will result from reaction of the third carboxyl groupwith one of the reactants of formulas II, III, and IV.) This branchingis believed to be detrimental to the performance of the molecule as athickener for latex compositions. Thus, techniques to reduce thisbranching and produce compositions comprised predominantly of compoundsof formula I should be employed in preparing the compounds of thisinvention.

Techniques to reduce branching include maintaining a comparatively lowconcentration of free epichlorohydrin in the reaction mixture. This canbe done by using less than the stoichiometric amount of epichlorohydrinor by slow addition of the stoichiometric amount of epichlorohydrin. Inthe former case, there will be excess alkoxide present that should berecovered and recycled to maintain an efficient production process. Inthe latter case, slow addition of the epichlorohydrin will reduce therate of product throughput in the reactor vessel.

Another useful technique is to introduce a reactant which will competewith the epichlorohydrin in the branching reaction. For example, wateror an alkylating agent can react with the alkoxide group of theintermediate alkoxide compound set forth above. If water reacts with thealkoxide intermediate, branching is inhibited because the alcohol groupis not as reactive with free epichlorohydrin as the alkoxide group ofthe alkoxide intermediate. Typical concentrations of water in thereaction medium range from 100 ppm to 2000 ppm water in the reactionsolvent. If a lower alkyl alkylating agent reacts with the alkoxideintermediate, the alkoxide is capped with a lower alkyl group, thuspreventing reaction (i.e., a sort of chain stopping effect) with freeepichlorohydrin or the reaction product of epichlorohydrin with thehydrophobe alkoxide R¹ --(O--A')_(a) --O⁻ and/or R⁶ --(O--A")_(c) --O⁻.

The reaction to produce the associative thickener is accomplished in thepresence of a solvent for the reactants and the reaction product. In thecontext of this invention, such a solvent will be an organic solventthat is chemically inert with respect to the reactants and which willform a low boiling azeotrope with water at the pressure chosen for thedistillation of the azeotrope. Such an azeotrope is one which boils at atemperature below the boiling points of both the organic solvent andwater. Typically, the organic solvent will be a hydrocarbon solvent,i.e., one consisting solely of carbon and hydrogen atoms, or anoxygenated hydrocarbon solvent, e.g., one consisting solely of carbon,hydrogen, and oxygen and having less than one oxygen atom per carbonatom. Preferred organic solvents are the higher alkanes, e.g., hexane,heptane, or nonane, aromatic hydrocarbons, e.g., benzene, toluene, orm-xylene, and ketones, e.g., 2-butanone, 2-pentanone, or 2 heptanone.The reaction product will, thus, be a solution of the associativethickener in organic solvent. The amount of organic solvent willtypically provide a solution at a solids content of about 10% to about80% by weight, more typically about 20% to about 60% by weight. Thesolution of associative thickener and water will be at a temperatureabove the boiling point of the low boiling azeotrope that will form atthe chosen distillation pressure from the organic solvent and the addedwater. It will typically also be at or below the boiling point of theorganic solvent and the water to keep either of these from flashing off.Thus, if the reaction to form the associative thickener is above allthree of those temperatures, the reaction mixture containing thereaction product can be cooled to a temperature that is above theboiling point of the low boiling azeotrope that will form at the chosendistillation pressure from the organic solvent and the added water, butno higher than the boiling points of water and the organic solvent atthat pressure. It is also possible to coot the reaction product afterthe reaction and reheat to a temperature above the boiling point of thelow boiling azeotrope that will form at the chosen distillationpressure. Such reheating is inefficient from the standpoint of energyconsumption (i.e., cooling and reheating wastes the heat stored in thehot reaction product), but reheating may be desirable if storage of thereaction product in organic solvent solution is desired prior topreparation of the concentrate. The pressure within the vessel duringthe distillation of the azeotrope can be ambient pressure, i.e.,atmospheric, or an elevated or reduced pressure may be employed,provided the azeotrope is still a low boiling azeotrope at the pressurechosen. The pressure is preferably atmospheric and the preferred solventis toluene.

Water is added to said solution and collection of the azeotrope of waterand said organic solvent is begun. The rate of addition of water isadjusted so the rate of addition of water is sufficient to replace saidazeotrope with water. This rate of addition should also take intoaccount any reflux of the azeotrope. In other words, if not all of theazeotrope is collected as distillate, the water in that portion of theazeotrope that is returned to the mixture must be counted as water thatis added to the mixture. If the rate of addition of water is too slow,the solids content of the mixture will become so great that theviscosity of the mixture will become unstirrable.

The rate of addition of water must be insufficient to cause a secondphase to form in the resulting mixture of said solution and said water.It has been found that if the rate of water addition is too fast, anoil-in-water emulsion will form. The presence of an oil-in-wateremulsion can be detected by the milky appearance of such an emulsion.The presence of the oil-in-water emulsion makes distillation of theorganic solvent extremely difficult, if not impractical. Thus, the rateof water addition should be controlled to at least replace the azeotropeformed, but to maintain the bulk of the polymer in true solution.Typically, water should be added to the solution of the reaction productat a rate of about 0.1 to about 1.0 parts per one hundred parts ofreaction product solution per minute, more typically from about 0.2 toabout 0.5 parts per one hundred parts of reaction product solution perminute (and there is essentially no reflux of azeotrope to returndistilled water to the mixture, i.e., essentially all azeotrope vapor iscollected as distillate). The azeotrope can be treated to separate thewater from the organic solvent, e.g., by decanting the organic solventwhen it is immiscible with water, and the separated water can be reusedas all or part of the water added to the solution of associativethickener in organic solvent.

It has been found that, as azeotrope is collected as distillate, thetemperature of the reaction mixture will fall as a result of the coolingprovided by the evaporation of the azeotrope, even if the set point ofthe heating medium is maintained at about the boiling point of thewater. It is preferred to allow the temperature of the reaction mixtureto fall to about the boiling point of the azeotrope, e.g., with tolueneand at atmospheric pressure, the temperature will fall to about 85° C.After the temperature has fallen and most of the organic solvent hasbeen removed, the temperature will begin to rise again. It has furtherbeen found that once the temperature begins to rise again, the rate ofwater addition can be increased, e.g., typically to a rate between about0.5 parts and 1.5 parts per hundred parts of reaction product solutionper minute, more typically about 0.75 to about 1.25 parts, without theformation of an oil-in-water emulsion.

When the level of organic solvent in the mixture has been reduced to thedesired level, e.g., typically less than about 0.5% by weight, moretypically less than about 0.1% by weight, and most typically less thanabout 0.05% by weight, distillation is discontinued (unless distillationof water is desired to raise the solids content of the product).Generally, the process of this invention results in a product having alower residual solvent as compared to simple vacuum distillation of theorganic solvent alone, i.e., not as an azeotrope. The solids content ofthe product can be adjusted by the distillation of water from themixture or the addition of water after distillation is discontinued. Thefinal solids content of the concentrate will typically be about 20% byweight to about 70% by weight, more typically 25% to about 50%, evenmore typically about 25% by weight to about 35% by weight. A surfactantcould be added to the concentrate to reduce the viscosity of theconcentrate and thus allow higher solids. The concentrate will typicallyhave a viscosity of less than about 15,000 cps (measured at 25° C. witha Brookfield Thermosel viscometer with a 3# spindle) more typically fromabout 2,500 cps to about 7,500 cps, and most typically about 4,000 cpsto about 6,000 cps. Thickener concentrate products according to theinvention can be sold commercially as aqueous-based compositionscontaining from about 35% to about 40% by weight thickener and havingBrookfield viscosities ranging from about 400-20,000 cps. The thickenersaccording to the invention afford commercial products which are higherin solids and are easier to handle because of their lower viscosities.

Aqueous compositions comprised of thickeners according to the inventionare also part of the invention. These compositions are comprised ofwater and a thickening-effective amount of one or more compounds offormula I. A thickening-effective amount is any amount required to bringthe viscosity of the aqueous composition within the range desired forthe intended application, e.g., a Brookfield viscosity of from about3,000 to about 5,000 cps (spindle #3, @ 30 r.p.m.). This amount willtypically be from about 1 to about 50% by weight of compounds accordingto the invention.

It is an advantage of this invention that an aqueous concentrateaccording to the invention need not contain a viscosity modifier whichis a compound, e.g., one selected from the group consisting of a liquidpolyol, a liquid ethoxylated or propoxylated C₁₋₈ alcohol, or a liquidethoxylated or propoxylated C₁₋₈ carboxylic acid. It is within thebroadest scope of the invention to add a viscosity modifier to theconcentrate, but such an addition is not preferred. A liquid polyol isany compound having two or more --OH groups which is a liquid at roomtemperature, examples of which include but are not limited to ethyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol.A liquid ethoxylated or propoxylated C₁₋₈ alcohol is any aliphaticalcohol ethoxylated or propoxylated to any degree of ethoxylation orpropoxylation and which is a liquid. Compounds in which the --OH groupof the liquid ethoxylated or propoxylated C₁₋₈ alcohol is etherifiedwith a C₁₋₄ alkyl group are also included in this group. A liquidethoxylated or propoxylated C₁₋₈ carboxylic acid is any aliphaticcarboxylic acid ethoxylated or propoxylated to any degree ofethoxylation or propoxylation and which is a liquid. Specific viscositymodifiers include butoxy triglycol (triethylene glycol monobutyl ether),butyl carbitol (diethylene glycol monobutyl ether), or 1,2-propyleneglycol. Any such compounds which contribute to the volatile organiccontent of the concentrate should be avoided.

The thickeners according to the invention are very efficient inincreasing the high shear and low shear viscosities of latexes or latexpaint compositions into which they have been incorporated. Latexes areemulsions or dispersions of water insoluble polymers in water. Latexpaint compositions typically contain at least an aqueous emulsion ordispersion of a water insoluble polymer, a pigment, a pigmentdispersant, a thickener to control the viscosity and improve theleveling and flow characteristics of the paint, and a preservative whichis effective in controlling the growth of microorganisms. Present paintindustry standards call for a latex paint having an ICI viscosity offrom about 0.8 to about 3.0 poise and a Stormer viscosity of from about90 to about 110 KU. The ICI viscosity is a high shear viscosity and ismeasured on the ICI (Research Equipment Limited) Cone and PlateViscosimeter at a shear rate of about 10,000 sec⁻¹. The Stormerviscosity is given in Krebs Units (KU) and is measured according to ASTMD662-81. Examples of the latexes which can be thickened with thethickeners according to the invention are those disclosed in U.S. Pat.No. 4,079,028 at column 12, line 64, to column 14, line 7, the entirecontents of which are incorporated herein by reference.

The thickening ability of the compounds according to the invention canvary with the type of substance to be thickened. For example, somecompounds may be very efficient at thickening acrylic latexes and not asefficient at thickening styrene-acrylic latexes while others may exhibitthe opposite behavior. In addition, the thickening ability of aparticular compound may also change when that compound is used in apaint formulation as opposed to a composition comprising only latex andwater.

For most commercial applications, a latex is thickened by adding asufficient amount of an aqueous composition according to the inventionto a latex to bring the ICI viscosity into the 0.8 to 3.0 poise rangeand the Stormer viscosity into the 95 to 105 KU. Typically this amountwill be in the range of from about 0.1% to about 10% of the thickeneraccording to the invention by weight of latex polymer solids andpreferably between 1% and 3% by weight of latex polymer solids. Thefollowing example is meant to illustrate, but not limit, the invention.

EXAMPLE 1

To a reactor equipped with a stirrer, nitrogen inlet tube, and adistillation head, add 36.8 parts by weight of tridecyl alcoholethoxylate (nominal 100 ethyleneoxy units per mole of ethoxylate), 22parts by weight of polyethylene glycol having a molecular weight ofabout 8,000 grams/mole and 40 parts by weight of toluene. To thismixture, added 1 part by weight of an aqueous solution containing 50% byweight sodium hydroxide. The contents of the reactor are then heated toazeotropically distill off most of the water with stirring and nitrogengas sparging. The conditions of distillation should be such that about0.1 to about 0.15% by weight of water remain in the toluene solution.The solution is then cooled to 80° C. after which 0.75 parts by weightof epichlorohydrin is added. The reaction mixture is then maintained at80° C. for two hours. The temperature is then raised to about 100° C.and then allowed to react until the viscosity is about 880 cps (asmeasure by Brookfield Thermosel at 70° C. with #3 LV spindle). Theepoxide titration should be approximately zero. (A 4.0 gram aliquot ofthe reaction mixture and 4 grams of tetraethylammonium bromide can bedissolved in 50 ml of glacial acetic acid and the resulting solutiontitrated with a 0.1036 N HClO₄ in glacial acetic acid solution to amethyl violet end point for the amount of epoxide (epoxy titration). Thereaction mixture is then neutralized to a substantially neutral pH(about pH 7) with 0.5 parts by weight of 70% aqueous glycolic acid.

The reactor set temperature is then set to 100° C. and water is added ata rate of 0.2 to 0.5 parts per minute. A toluene/water azeotrope shouldstart to distill immediately and is collected. If the mixture foams soas to fill the reactor, water addition should be discontinued until thefoam subsides. The temperature of the mixture should drop to 80-85° C.When the temperature reaches this range, the rate of water is thenincreased to 1 part per minute. The temperature should rise to 100° C.when most of the toluene has been removed. Maintain distillation andwater addition for one hour after temperature reaches 100° C. Adjustsolids of product to 30% by distillation of water after water additionis complete or continuing water addition after distillation is complete.

What is claimed is:
 1. A process of preparing a concentrate which isuseful as a thickener for aqueous compositions comprising the stepsof:A) preparing a solution of an associative thickener compound in anorganic solvent capable of forming a low boiling azeotrope with water,said solution being essentially free of water, at a temperature abovethe boiling point of said low boiling azeotrope, B) adding water to saidsolution while distilling an azeotrope of water and said organicsolvent, and, C) maintaining the addition of water at a rate sufficientto replace said azeotrope with water, but insufficient to cause a secondphase to form in the resulting mixture of said solution and said water.2. The process of claim 1 wherein said organic solvent is selected fromthe group consisting of hydrocarbon solvents and oxygenated hydrocarbonsolvents.
 3. The process of claim 1 wherein said organic solvent isselected from the group consisting of C₆ -C₉ alkanes and benzene and C₁-C₄ alkyl-substituted benzenes.
 4. The process of claim 1 wherein saidorganic solvent is toluene.
 5. The process of claim 1 wherein said wateris added to the solution, at least initially at a rate of from about 0.1to about 1.0 parts per one hundred parts of reaction product solutionper minute.
 6. The process of claim 1 wherein said water is added to thesolution, at least initially at a rate of from about 0.2 to about 0.5parts per one hundred parts of reaction product solution per minute. 7.The process claimed in claim 1 wherein there is essentially no reflux ofazeotrope to return distilled water to the mixture.
 8. The process ofclaim 1 wherein the temperature of the reaction mixture falls to aboutthe boiling point of the azeotrope after the beginning of addition ofsaid water.
 9. The process of claim 8 wherein the rate of water additionis increased after said temperature falls to the boiling point of saidazeotrope and begins to rise therefrom.
 10. The process of claim 9wherein said increased rate is between about 0.5 parts and 1.5 parts perhundred parts of reaction product solution per minute.
 11. The processof claim 9 wherein said increased rate is between about 0.75 to about1.25 parts.
 12. The process of claim 1 wherein the level of organicsolvent in said mixture is reduced to less than about 0.5% by weight.13. The process of claim 1 wherein the level of organic solvent in saidmixture is reduced to less than about 0.05% by weight.
 14. The processof claim I wherein the solids content of the product of said process isfrom about 20% by weight to about 70% by weight.
 15. The process ofclaim 1 wherein the solids content of the product of said process isfrom about 25% by weight to about 35% by weight.
 16. The process ofclaim 1 wherein the viscosity of the product of said process is lessthan about 15,000 cps.
 17. The process of claim 1 wherein said solutionof an associative thickener compound in an organic solvent capable offorming a low boiling azeotrope with water is about 10% to about 80% byweight of said associative thickener.
 18. The process of claim 1 whereinsaid solution of an associative thickener compound in an organic solventcapable of forming a low boiling azeotrope with water is about 20% toabout 60% by weight of said associative thickener.
 19. The process ofclaim 16 wherein said viscosity from about 2,500 cps to about 7,500 cps.20. The process of claim 16 wherein said viscosity is from about 4,000cps to about 6,000 cps.